MUTILATION AND REGENERATION 



389 



such facts as are known, and to realize the difficulties 

 in the way of accurately comprehending them. 



I. The mutilated organism restores its symmetry by a 

 rearrangement of its substance and recovers its size by 

 subsequent growth. 



This is seen in lowly organisms only. Thus, when the 

 protozoan Stentor coeruleus is cut transversely into 



FIG. 143. Stentor coeruleus. a, Cut into three pieces; 6, regeneration of 

 anterior piece; c, regeneration of middle piece; d, regeneration of posterior piece. 

 (After Gruber.) 



several segments, each fragment containing nuclear sub- 

 stance, transforms itself into a more or less perfect 

 diminutive of the original in the course of a few hours and 

 is then ready to grow to its normal size. Fragments 

 without nuclear material soon die. 



A similar adjustment is seen in Hydra. When this 

 organism is transversely cut, the anterior half lengthens 

 and develops a new base, the posterior half also lengthens 

 and develops new tentacles, so that two new hydras are 

 formed. If a fragment be cut out of the centre of a 

 hydra by two parallel transverse incisions, the ends 



